One conventional method of obtaining isobutylene is from a crude C4 stream (CC4) produced as a co-product of ethylene in a steam cracking process. The crude C4 stream is a mixture of C4 olefins, di-olefins and saturated hydrocarbons, with the quantity of CC4 and the relative proportions of the CC4 components dependent on the cracker feedstock and operating conditions. Typically, a series of extraction steps are performed to separate the isobutylene from the CC4.
Isobutylene may also be obtained through the dehydrogenation of isobutane (“the iBDH process”). In the iBDH process, isobutane may be decomposed over a catalyst to produce isobutylene and hydrogen. Separation and recovery of isobutylene from the reactor effluent of the iBDH process is performed by reacting the effluent with an alcohol to form an ether, which is then separated from the remainder of the reactor effluent. Isobutylene is recovered following the cracking of the ether, which also regenerates the alcohol.
Isobutane may also be used to produce alkanes of a sufficient octane number and vapor pressure for gasoline-type fuels through alkylation. In alkylation, isobutane may be reacted with olefins, such as butenes or propylene, to form branched alkanes. Traditionally, the olefins used in alkylation have been obtained from other processes used in the petrochemical or petroleum refining industries. For example, propylene and butenes may be produced in steam crackers utilizing naphtha as a feedstock, while propylene may also be obtained as a byproduct of fluid catalytic cracking.